The only thing I can add to Sully's method which helped me out greatly is to spam Rainbow in the Dark. Since there are no chords, just spam all the buttons the song plays really fast and you'll hit them all and get 100% by the end of the song. It doesn't matter if you keep hearing and seeing misses, you are obviously still hitting the notes. To make sure you are, be in the challenge so you can see your %. This song gave me some trouble compared to the first two.